show selectively permiable membrane works
Answers
Students learn that engineers develop different polymers to serve various functions and are introduced to selectively permeable membranes. In a warm-up activity, they construct models of selectively permeable membranes using common household materials, and are reminded about simple diffusion and passive transport. In the main activity, student pairs test and compare the selective permeability of everyday polymer materials engineered for food storage (including plastic grocery bags, zipper sandwich bags, and plastic wrap) with various in-solution molecules (iodine, corn starch, food coloring, marker dye), assess how the polymer’s permeability relates to its function/purpose, and compare that to the permeability of dialysis tubing (which simulates a cell membrane).
The presence of a selectively permeable membrane allows the cell to exercise control over the quantum, timing and rate of movement of these molecules. Movement across a selectively permeable membrane can occur actively or passively. For example, water molecules can move passively through small pores on the membrane.